Center cylinder ejection assist

ABSTRACT

A method of ejecting a container from a blow mold comprises the steps of: opening a blow mold containing a container, the blow mold comprising a pair of pistons having a head and a heel, an end cap disposed behind the heel, and a pair of ejector rods, each ejector rod coupled to a different piston; simultaneously with the opening forcing a fluid against each head of each of the pair of pistons, extending each of the ejector rods to maintain contact with an opposite side of a center portion of the container in the blow mold and pushing the container from the blow mold; and forcing a fluid against the heel of each of the pair of pistons operative to retract the pair of ejector rods away from the container when the container is separated from the blow mold.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to the blow-moldingcontainer manufacturing process and more particularly to ejectingblow-molded containers from molds.

[0003] 2. Related Art

[0004] One method of producing hollow plastic containers, such asbottles, is blow-molding. Blow-molding is a process of forming a moltentube of thermoplastic material, then blowing up the tube with compressedair to conform to the interior of a chilled blow mold. The most commonmethods are extrusion, injection, and injection-stretch blow molding.

[0005] The extrusion method is usually used to form containers weighingmore than 12 grams, such as containers for food and laundry detergents.The method uses a continuously running extruder with a tuned die headthat forms the molten plastic tube. The tube is then pinched between twomold halves. A blow pin or needle is inserted into the tube andcompressed air is used to blow up the part to conform to the chilledmold interior. The accumulator-extrusion method is similar, however, themolten plastic material is accumulated in a chamber prior to beingforced through a die to form the tube.

[0006] Injection blow molding is usually used when accuratewall-thickness and/or a high-quality neck finish is needed, or when apolymer cannot be extruded. The method is a process of injection moldinga preform (similar in shape to a test tube), then taking the temperedpreform to a blow mold to be filled with compressed air to conform tothe interior of the blow mold.

[0007] Stretch blow molding is used for polymers that are difficult toblow, such as crystalline and crystallizable polymers, e.g.polypropylene and polyethylene terephthalate. Stretch blow molding canbe a single-stage process similar to standard injection blow molding, byadding the element of stretch prior to blow forming. Also, a two-stepprocess is possible, where a preform is made in an injection moldingmachine, then taken to a reheat-stretch blow molding machine for preformreheating and final blow forming in a blow mold.

[0008] After a bottle is blow-molded, the mold is opened to allow thebottle to fall out for further processing. Often, however, part of thebottle sticks to the mold. When the bottle sticks to the mold, severalproblems can occur. First, some manufacturing systems have a safety stopswitch. When the bottle becomes stuck in a mold, the manufacturingswitch is triggered shutting down the manufacturing line and causingdelays in the manufacturing process. Second, the bottle may eventuallyfall on its own, or may be un-stuck by a conventional ejection-assistsystem, but deformation of the bottle can occur as a result of sticking,for example, causing the bottle to bend around the sticking part beforeultimately falling. A bent bottle will cause problems further down inthe manufacturing process, which relies on properly formed bottles inorder to operate efficiently.

[0009] This is particularly a problem for dual cavity systems. In a dualcavity system, two containers are molded simultaneously. The twocontainers are typically joined at the top finish end through a moil toform a “log.” In downstream operations, subsequent to molding, trimmingand finishing occurs, where, for example, the moil is trimmed off asscrap. The downstream trimming and finishing requires several steps. Forexample, the log must be transported to a trimmer. In the trimmer, acutter cuts the moil from the top of each container. The neck is thenfinished by, for example, reaming or cleaning of the opening. Inaddition, the flash, or scrap around the seam of the containers must betrimmed either before or after the individual containers are generatedby cutting from the log. In many of these downstream operations, properorientation of the log is required. Orientation of the log can beperformed by automated machinery. However, if the log is bent, forexample at the moil, the automated machinery may be unable to handle thebottles, i.e. the bent log does not properly fit in the automatedmachinery. As a result, the downstream processes are affected. Forexample, the bent log may become lodged in the trimmer, cutter orcleaner resulting in machine malfunction and system downtime.Alternatively, the container may be improperly cut leading to anincrease in waste. In either event, system efficiency is decreased.

[0010] One conventional ejection-assist system is a pneumatic ejectionsystem. It operates on dual-cavity container “logs” where the twocontainers are joined at the neck by a moil in the mold. The bottom ofeach bottle has a tail-flash extending from it. The conventionalejection-assist system has ejector rods that hold the tail-flash whilethe mold opens. The ejector rods push the log from the mold and then areretracted by timed air-cylinders. However, because the ejector rods pushthe log from its ends, if the moil in the middle is stuck to the mold,the force of the push will bend the log at the middle, causing problemsfurther down the manufacturing line.

[0011] What is needed then is an improved system and method for ejectingblow-molded containers that overcome the shortcomings of conventionalsolutions.

BRIEF SUMMARY OF THE INVENTION

[0012] In summary, an exemplary embodiment of the present inventionprovides an improved method of ejecting blow-molded containers fromtheir molds by pushing against the center portion of the moldedcontainer. This prevents the container from sticking to the mold andbending.

[0013] In an exemplary embodiment, the present invention can be anejection-assist apparatus for ejecting a container from a mold cavitycomprising: a mold half cooperating with a second mold half to form themold cavity; an ejector rod having a contact end for contacting thecontainer and a back end; a cylinder body around the ejection rod; apiston having a heel and a head and coupled to the back end of theejector rod; a cylinder barrel around the piston having an end cap andan front end, the piston being slidable within the cylinder barrel, andthe front end contiguous with the cylinder body; a forward fluid passagehaving a blowing end and a back end, the blowing end operative to blowfluid into the cylinder barrel through the end cap on the head of thepiston and the back end connectable to a first external fluid supply;and a return fluid tube having a blowing end and a back end, the blowingend operative to blow fluid into the barrel cylinder on the heel of thepiston and the back end connectable to a second external fluid supply,wherein blowing a fluid on the head of the piston moves the piston andthe ejector rod into an extended position and blowing a fluid on theheel of the piston moves the piston and the ejector rod into a retractedposition.

[0014] In another exemplary embodiment, the present invention can be amethod of ejecting a container from a blow mold comprising the steps of:opening a blow mold containing a container, the blow mold comprising apair of pistons having a head and a heel, an end cap disposed behind theheel, and a pair of ejector rods, each ejector rod coupled to adifferent one of the pistons; simultaneously with the opening forcing afluid against each head of each of the pair of pistons, extending eachof the ejector rods to maintain contact with an opposite side of acenter portion of the container in the blow mold and pushing thecontainer from the blow mold; and forcing a fluid against the heel ofeach of the pair of pistons operative to retract the pair of ejectorrods away from the container when the container is separated from theblow mold.

[0015] Further objectives and advantages, as well as the structure andfunction of preferred embodiments will become apparent from aconsideration of the description, drawings, and examples.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The foregoing and other features and advantages of the inventionwill be apparent from the following, more particular description of apreferred embodiment of the invention, as illustrated in theaccompanying drawings wherein like reference numbers generally indicateidentical, functionally similar, and/or structurally similar elements.

[0017]FIG. 1 depicts top view cross-section of an exemplary embodimentof the apparatus in a extended position according to the presentinvention;

[0018]FIG. 2 depicts an end view cross-section of an exemplaryembodiment of the apparatus in an retracted position according to thepresent invention; and

[0019]FIG. 3 depicts an end view cross-section of an exemplaryembodiment of the apparatus in a extended position according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

[0020] Embodiments of the invention are discussed in detail below.- Indescribing embodiments, specific terminology is employed for the sake ofclarity. However, the invention is not intended to be limited to thespecific terminology so selected. While specific exemplary embodimentsare discussed, it should be understood that this is done forillustration purposes only. A person skilled in the relevant art willrecognize that other components and configurations can be used withoutparting from the spirit and scope of the invention. All references citedherein are incorporated by reference as if each had been individuallyincorporated.

[0021]FIG. 1 depicts a top view cross section 100 of an exemplaryembodiment of the present invention. The dual-cavity blow mold consistsof two halves, each half made of a back plate 102 and a cavity block104. The bottle “log” 106 consists of two containers 103 a and 103 b,for example, bottles, joined at the neck by a moil 108. An ejectionassist assembly is placed in each half of the blow mold. The assemblyincludes an ejector rod 110. The ejector rod 110 comes in contact withthe moil 108 during the ejection assist process and pushes the moil 108out of the cavity block 104.

[0022] The apparatus that drives the ejector rod 110 is housed, in anexemplary embodiment, in the back plate 102 of the mold. The apparatusis made up of a cylinder body 112 that surrounds a back portion of theejector rod 110, and a cylinder barrel 114 behind, and coupled to, thecylinder body 112. The apparatus is further comprised of a piston 116,housed inside the cylinder barrel 114 and directly behind and fastenedto the ejector rod 110, and two fluid fittings 118 and 120 that causethe piston 116 to move back and forth along the axis of the ejector rod110 by using forward fluid passage 122 and return fluid tube 124,respectively, as will be explained in further detail below with respectto FIGS. 2 and 3. The fluid passage 122 and tube 124 are sealed, in anexemplary embodiment, with a number of “O” rings 126. An end cap 128which is part of the back plate 102 fills the inner diameter of thecylinder barrel 114 at the back of the apparatus, and has a hole for theforward air passage 122. In an exemplary embodiment, the cylinder barrel114 and the cylinder body 112 can be one single piece.

[0023] In the exemplary embodiment described herein, the fluid used tomove the assembly between the extended and retracted positions is air.In other embodiments, other fluids can be used such as other gases, forexample, nitrogen or inert gases, or liquids, for example, a hydraulicfluid. Fluids can be supplied from a fluid source outside the mold ormolding machine such as for example, a pneumatic air line. The controlof the supply of fluid to the forward and return fluid tubes isconducted externally to the ejector system assembly. Fluid in-flow maybe microprocessor controlled and can be part of the overall controlmechanism of the molding system of which the invention forms a part.Such control systems are known in the art and can be suitably modifiedby the skilled artisan using known techniques.

[0024]FIG. 2 depicts an end view cross section 200 of an exemplaryembodiment of the apparatus in a retracted position according to thepresent invention. The pair of ejector rods 110 are retracted and are incontact with the moil 108. When in the retracted position, there is aspace 202 between the heel of the piston 116 and the back of thecylinder body 112. The forward air passage 122 has its blowing end 122 ain contact with the back of the piston 116. As the mold opens, the pairof ejector rods 110 extend inwardly to maintain contact with the moil108 and push it from the mold cavity block 104. The extension of therods 110 occurs when air is forced through the air fitting 118, throughthe forward air passage 122, and against the back of the piston 116,pushing the piston 116 forward towards the mold and closing space 202.

[0025]FIG. 3 depicts an end view cross section 300 of an exemplaryembodiment of the apparatus in an extended position according to thepresent invention. The piston 116 has moved the ejection assist assemblyforward. While the assembly is in the extended position, there is aspace 302 between the end cap 128 and the head of the piston 116. In anexemplary embodiment, the piston 116 pushes the ejector rod 110 forwardapproximately 0.25 to 0.5 inches or more. The blowing end 124 a of thereturn air tube 124 is now in contact with the heel of the piston 116.To retract the assembly, air is then forced through air fitting 12, andthrough return air tube 124 to push back against the heel of piston 116,which causes the piston 116 and the attached ejector rod 110 to moveback away from the cylinder body 112 and back toward the end cap 128.

[0026] In an exemplary embodiment, the timing of the ejection assistaction is very important. The action is begun at about the exact momentthat the mold itself begins to open. This precise timing prevents themoil 108 from being dented or distorted when ejected by the ejector rods110.

[0027] Another feature of the present invention is that ejection assistassembly, although mounted within part of the mold, is easilyaccessible, in an exemplary embodiment, by removing the back plate ofthe mold. Further, the air fittings do not need to be attached to thecylinder that houses the piston. Instead, the forward air fitting isdirected at the back of the piston, but is not attached to it.

[0028] Another feature of the present invention is that the location ofthe ejection mechanism is not restricted to the back plate. In anexemplary embodiment, the ejection mechanism can be part of the moldbody. Further, the ejection mechanism does not need to be in the centerof the mold. It can be placed anywhere in the mold where it is needed.Additionally, there can be more than one ejection mechanism in the mold,which is useful especially for large containers.

[0029] The embodiments illustrated and discussed in this specificationare intended only to teach those skilled in the art the best way knownto the inventors to make and use the invention. Nothing in thisspecification should be considered as limiting the scope of the presentinvention. All examples presented are representative and non-limiting.The above-described embodiments of the invention may be modified orvaried, without departing from the invention, as appreciated by thoseskilled in the art in light of the above teachings. It is therefore tobe understood that, within the scope of the claims and theirequivalents, the invention may be practiced otherwise than asspecifically described.

What is claimed is:
 1. An ejection-assist apparatus for ejecting acontainer from a mold cavity comprising: a mold half cooperating with asecond mold half to form the mold cavity; an ejection assist apparatusin said mold half, said ejection assist apparatus comprising: an ejectorrod having a contact end for contacting the container and a back end; acylinder body around said ejection rod; a piston having a heel and ahead and coupled to said back end of said ejector rod; a cylinder barrelaround said piston having an end cap and a front end, said piston beingslidable within said cylinder barrel, and said front end contiguous withsaid cylinder body; a forward fluid passage having a blowing end and aback end, said blowing end operative to blow fluid into said cylinderbarrel through said end cap on said head of said piston and said backend connectable to a first external fluid supply; and a return fluidtube having a blowing end and a back end, said blowing end operative toblow fluid into said barrel cylinder on said heel of said piston andsaid back end connectable to a second external fluid supply, whereinblowing a fluid on said head of said piston moves said piston and saidejector rod into an extended position and blowing a fluid on said heelof said piston moves said piston and said ejector rod into a retractedposition.
 2. The ejection-assist apparatus of claim 1, wherein the fluidis air.
 3. The ejection-assist apparatus of claim 1, wherein the ejectorrod is aligned for contacting said contact end with a center portion ofa container log made in the mold cavity.
 4. The ejection-assistapparatus of claim 1, further comprising an open space between said headof said piston and said end cap when said piston is in an extendedposition.
 5. The ejection-assist apparatus of claim 1, furthercomprising an open space defined by said heel of said piston, saidcylinder body and said ejector rod when said piston is in a retractedposition.
 6. The ejection-assist apparatus of claim 1, wherein an insidediameter of said cylinder barrel is larger than an inside diameter ofsaid cylinder body.
 7. The ejection-assist apparatus of claim 1, whereinsaid return fluid tube directs fluid through said cylinder body.
 8. Theejection-assist apparatus of claim 1, wherein the mold half comprises aback plate and a cavity block, wherein said ejection-assist apparatus isin said back plate.
 9. The ejection-assist apparatus of claim 8, whereinsaid back plate comprises said cylinder body and said cylinder barrel.10. The ejection-assist apparatus of claim 8, further comprising aforward fluid fitting attached to said back plate and connected to saidforward fluid passage; and a return fluid fitting attached to said backplate and connected to said return fluid tube.
 11. The ejection-assistapparatus of claim 1, further comprising a forward fluid fittingattached to said mold body and connected to said forward fluid passage;and a return fluid fitting attached to said mold body and connected tosaid return fluid tube.
 12. The ejection-assist apparatus of claim 1,wherein said mold cavity is adapted for molding a container log thatcomprises a first container and a second container joined by a moil. 13.The ejection-assist apparatus of claim 12, wherein said ejector rod ispositioned in said mold half to contact said moil.
 14. Theejection-assist apparatus of claim 1, wherein the mold half comprises aback plate and a cavity block, wherein said ejection-assist apparatus isin said cavity block.
 15. The ejection-assist apparatus of claim 1,wherein at least two ejection-assist apparatuses are disposed in saidmold half.
 16. A method of ejecting a container from a blow mold, themethod comprising the steps of: opening a blow mold containing acontainer, said blow mold comprising a pair of pistons having a head anda heel, an end cap disposed behind said heel, and a pair of ejectorrods, each ejector rod coupled to a different one of said pair ofpistons; simultaneously with said opening forcing a fluid against eachhead of each of said pair of pistons, extending each of said ejectorrods to maintain contact with an opposite side of a center portion ofthe container in said blow mold and pushing the container from said blowmold; and forcing a fluid against said heel of each of said pair ofpistons operative to retract said pair of ejector rods away from thecontainer when the container is separated from said blow mold.
 17. Themethod of claim 16, wherein said ejector rods are extended 0.25 to 0.5inches.
 18. The method of claim 16, wherein said ejector rods areextended more than 0.5 inches.
 19. The method of claim 16, wherein saidfluid is air.
 20. The method of claim 16, wherein said ejector rods arealigned for contacting a center portion of a container made in the blowmold.
 21. The method of claim 16, wherein said pistons retract into anopen space between said head of said piston and said end cap.
 22. Themethod of claim 16, wherein said blow mold further comprises a cylinderbody around said ejector rod and wherein said pistons extend into anopen space defined by said heel of said piston, said cylinder body andsaid ejector rod.
 23. The method of claim 16, wherein the blow moldcomprises two halves, each half comprising a back plate and a cavityblock, wherein said end-cap is a part of said back plate and closes offone end of said cylinder body, each of said cylinder bodies are mountedin one of said back plates, and each of said ejector rods and saidpistons are housed in one of said back plates.
 24. The method of claim23, wherein said blow mold cavity block is adapted for molding acontainer that comprises a first container and a second container joinedby a moil.
 25. The method of claim 24, wherein said ejector rod ispositioned in said blow mold half to contact said moil.